Generally, a sliding nozzle device comprises a plurality of refractory plates, a plurality of receiving metal frames for fixedly holding respective ones of the refractory plates, a drive unit for driving one of the receiving metal frames, and pressure applying means for clamping the plates together to apply pressure between respective surfaces of the plates, wherein one of the plates is slidingly moved relative to the remaining plates to selectively open and close a nozzle hole so as to control a flow rate of molten steel, and, during use, a large pressure is applied between the respective surfaces of the plates to prevent leakage of molten steel from a gap between the plates. In the sliding nozzle device, each of the plates is fixedly held by a corresponding one of the receiving metal frame. Typically, the plate primarily comprises a plate brick having a nozzle hole, and includes one type in which a siding surface of the plate brick is tightly bound by a metal band, and another type in which a box-shaped metal casing is attached to the plate brick.
As shown in FIG. 7, one type of sliding nozzle device comprises: an upper plate 72; a lower plate 75; a fixed metal frame 73 mounted to a lower portion of an upper nozzle provided at a bottom of a molten metal vessel 71, to hold the upper plate 72; an opening-closing metal frame 74 provided in an openable/closable manner relative to the fixed metal frame 73; a sliding metal frame 76 provided between the fixed metal frame 73 and the opening-closing metal frame 74 to hold the lower plate 75; an elastic member (not shown) pressing the lower plate 75 against the upper plate 72; and a drive unit 79 for slidingly moving the sliding metal frame 76, wherein the sliding metal frame 76 is slidingly moved to adjust a level of opening based on a relative position between two nozzle holes 77, 78 formed in respective ones of the lower plate 75 and the upper plate 72 so as to control a flow rate of molten metal. The upper and lower plates 72, 75 are fixedly held by respective ones of the fixed metal frame 73 and the sliding metal frame 76. There are also other types, such as a type using three plates, a type having an integrated combination of a lower nozzle and a lower plate, and a type having an integrated combination of a lower plate and an immersion nozzle.
In such types of sliding nozzle devices, as means to fix the plate to the receiving metal frame, there are a longitudinally-pressing mechanism and a laterally-pressing mechanism. The longitudinally-pressing mechanism is primarily intended to prevent displacement of the plate due to a sliding force linearly applied thereto. However, during use, the plate is heated up to high temperatures to undergo thermal expansion, and a force resulting from the thermal expansion acts as a compression force to compress the plate in a longitudinal direction thereof, which is likely to cause the occurrence of a large crack extending in the longitudinal direction in the plate. Moreover, during use, due to the thermal expansion of the plate, a pressing force from the longitudinally-pressing mechanism less subjected to thermal expansion is relatively increased to cause a higher risk of the occurrence of the crack.
With a view to preventing the occurrence of the longitudinal crack as an disadvantage of the longitudinally-pressing mechanism, there has been proposed a technique designed to simultaneously implement the longitudinally-pressing mechanism and the laterally-pressing mechanism, wherein the laterally-pressing mechanism is adapted to apply a pressing force in a lateral direction of the plate using a cotter-type member, as disclosed, for example, in the following Patent Document 1. It is assumed that this technique has an advantage of allowing the occurrence of the longitudinal crack to be suppressed by the lateral pressing force (a laterally outward deformation of the plate due to the longitudinal pressing force to be suppressed by a laterally inward pressing force from the laterally-pressing mechanism) so as to prevent the occurrence of the crack extending from the nozzle hole of the plate in the longitudinal direction. As above, the laterally-pressing mechanism is generally used in combination with the longitudinally-pressing mechanism to complement the disadvantage of the sliding nozzle device employing only the longitudinally-pressing mechanism.
Further, the following Patent Document 2 discloses a clamping mechanism of a sliding nozzle device intended to be used for a refractory plate having a curved outer peripheral surface, wherein a plurality of pressing members arranged around an elliptical or oval-shaped refractory plate are link-connected to each other using pins, and a tension force is applied to the link-connected structure to allow the pressing members to fixedly clamp the refractory plate from a plurality of directions. An advantage of this clamping mechanism is described as follows. The refractory plate can be fixedly clamped from a plurality of directions using a small number of tensioning units to allow a clamping operation to be performed in a simple manner and completed within a significantly short period of time. In addition, there is not a need for providing a plurality of clamping mechanisms each having a different clamping direction as in conventional devices, which makes it possible to facilitate simplification in structure and eliminate a risk of the occurrence of inadvertently unclamped portion. Further, the refractory plate is approximately uniformly clamped over the entire outer periphery thereof, so that local stress on the refractory plate can be reduced as compared with conventional techniques.
[Patent Document 1] JP 2000-233274A
[Patent Document 2] Microfilm of Japanese Utility Model Application No. 55-027468 (JU 56 131966A)